Revert "Chrome fails in ajax.js tests because TestSwarm/Ngnix won't give HEAD requests any respect. Skip them rather than hear Swarmy call FAILURE on each run."

This reverts commit 9c5089a6.

These were not the droids we were looking for. Actually caused by a BrowserStack issue.

This is only a unit test fix because the bug was tangentially fixed by a different commit

Sizzle: account for external document contexts (such as iframes) in combinator checks. Fixes #12572.

I can't think of an uncontrived way to unit test this, it only occurs in IE when a BHO monkeys with the links.

This lets us still add the other offset components to the number so they're less wrong. Affects BlackBerry 5 and iOS 3, everyone else has gBCR.

Chrome fails in ajax.js tests because TestSwarm/Ngnix won't give HEAD requests any respect. Skip them rather than hear Swarmy call FAILURE on each run.

Thanks @vlakoff!

Retains the rooted-at-delegateTarget behavior fixed in #12383 by afd717df.